From owner-freebsd-multimedia@FreeBSD.ORG Fri Apr 15 08:15:08 2005 Return-Path: Delivered-To: freebsd-multimedia@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 3C14316A4CE for ; Fri, 15 Apr 2005 08:15:08 +0000 (GMT) Received: from ylpvm43.prodigy.net (ylpvm43-ext.prodigy.net [207.115.57.74]) by mx1.FreeBSD.org (Postfix) with ESMTP id B5D1143D41 for ; Fri, 15 Apr 2005 08:15:06 +0000 (GMT) (envelope-from julian@elischer.org) Received: from pimout3-ext.prodigy.net (pimout3-ext.prodigy.net [207.115.63.102])j3F8F6l8019486 for ; Fri, 15 Apr 2005 04:15:07 -0400 X-ORBL: [68.124.205.128] Received: from [192.168.2.2] (adsl-68-124-205-128.dsl.snfc21.pacbell.net [68.124.205.128])j3F8EaxG242466; Fri, 15 Apr 2005 04:14:46 -0400 Message-ID: <425F77EB.7080902@elischer.org> Date: Fri, 15 Apr 2005 01:14:35 -0700 From: Julian Elischer User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.5) Gecko/20050214 X-Accept-Language: en, hu MIME-Version: 1.0 To: Alexander Leidinger References: <20050410195645.GA2178@cnd.mcgill.ca> <20050414.021552.343134310.kazuhito@ph.noda.tus.ac.jp> <20050413172534.GF2178@cnd.mcgill.ca> <20050414161546.kwroviadwsw8k0w0@netchild.homeip.net> <425ED3F0.70603@elischer.org> <20050415095335.46kkjh7q4gkwook0@netchild.homeip.net> In-Reply-To: <20050415095335.46kkjh7q4gkwook0@netchild.homeip.net> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit cc: freebsd-multimedia@freebsd.org cc: Mathew Kanner Subject: Re: de-dma uaudio X-BeenThere: freebsd-multimedia@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Multimedia discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 15 Apr 2005 08:15:08 -0000 Alexander Leidinger wrote: > Julian Elischer wrote: > >> The low hardware layer already does DMA to move data out of the >> hardware to memory. The data gets copied from the user layer to an >> intermediate >> buffer and from there to the DMA buffers. There is no need to allocate >> DMA capable >> buffers for the intermediate layer. > > > I understand this as: > userland-mem -> kernel-mem -> dma-able-mem -> hardware > > So there's no zero-copy behavior? > userland-mem -> in-kernel-dma-able-mem -> hardware > or > userland-mem -> if(is_dmaable(userland-mem)) -> hardware > else -> in-kernel-dma-able-mem -> hardware > > While the amount of memory used as a sound buffer isn't that much for > todays > standards, it's still a memory transfer operation which could be avoided. I > don't know how much it would affect the latency (or if it affects it at > all), but not doing things which aren't necesssary/beneficial is always a > win (in some way) in my experience. > > Bye, > Alexander. > no-one is saying that it can't be optimised.. try follow a read command from a ugen fd all the way to the hardware.. it's just not something we've spent time to do.